Phytoplankton communities play a crucial role in marine ecosystems, serving as primary producers and key components of marine food webs. Understanding the size structure and functional types of phytoplankton in Indian coastal waters is essential for assessing ecosystem health and productivity. This brief overview aims to summarize the current knowledge on phytoplankton size structure and functional types in these waters. The size structure of phytoplankton in Indian coastal waters varies widely, ranging from picoplankton (<2 μm) to microplankton (>20 μm). Factors controlling phytoplankton size include nutrient availability, light intensity, temperature, and grazing pressure. Nutrient availability, particularly nitrogen and phosphorus, often limits phytoplankton growth and influences size distribution. Functional types of phytoplankton refer to different groups based on their ecological roles and physiological characteristics. Common functional types include diatoms, dinoflagellates, coccolithophores, and cyanobacteria. Diatoms are prevalent in nutrient-rich coastal waters, contributing significantly to primary production and forming the base of the food web. Dinoflagellates are known for their ability to form harmful algal blooms under certain conditions, impacting ecosystem dynamics and human health. Coccolithophores play a crucial role in carbon cycling and ocean acidification, while cyanobacteria are important nitrogen fixers, particularly in nutrient-poor waters. Various environmental factors, including temperature, salinity, nutrient availability, and grazing pressure, regulate the distribution and abundance of these functional groups. Anthropogenic activities, such as coastal development and pollution, can also influence phytoplankton communities and functional types, leading to shifts in ecosystem structure and function. Understanding the size structure and functional types of phytoplankton in Indian coastal waters is essential for ecosystem management and conservation efforts.